Investigating three sources of bias in hook-and-line surveys: survey design, gear saturation, and multispecies interactions

Abstract

Hook-and-line surveys can be used to estimate population trends in fish species where conventional methods such as trawl, acoustic, visual, or pot surveys cannot be applied. Hook-and-line surveys allow for the collection of biological information, but the resultant indices of abundance may be biased. We designed simulations to address concerns around survey design, hook saturation, and competition among species and found that catch per unit effort (CPUE) declined more slowly than population size across all scenarios. This hyperstability was most prominent when fish were found in high-density patches, and these scenarios have median absolute relative error values roughly three to five times greater than those with more even distributions of fish density. Despite hyperstability, the surveys still had statistical power to detect changes in abundance. Interspecific competition for hooks caused bias in survey results when one species was more aggressive than another. Taken together, our results indicate hook-and-line surveys fill a niche in survey methodologies, but their use and interpretation can be challenged by hyperstability and competition among species.Résumé : Les relevés à la ligne peuvent être utilisés pour estimer les tendances démographiques d'espèces de poissons quand des méthodes traditionnelles comme les relevés acoustiques, visuels, au chalut et au casier ne peuvent être employées. Si les relevés à la ligne permettent la collecte de renseignements biologiques, les indices d'abondance en découlant peuvent être biaisés. Nous avons conçu des simulations pour examiner les problèmes potentiels entourant la conception des relevés, la saturation des hameçons et la concurrence entre espèces et avons constaté que les captures par unité d'effort (CPUE) baissent plus lentement que la taille de la population pour tous les scénarios. Cette hyperstabilité est la plus prononcée quand les poissons se trouvent dans des groupements de haute densité, ces scénarios présentant des valeurs absolues médianes de l'erreur relative environ trois à cinq fois supérieures aux valeurs associées à des répartitions plus uniformes de la densité de poissons. Malgré l'hyperstabilité, les relevés ont la capacité statistique de détecter des variations d'abondance. La concurrence entre espèces pour les hameçons cause un biais dans les résultats des relevés quand une espèce est plus agressive qu'une autre. Collectivement, nos résultats indiquent que les relevés à la ligne ont leur place parmi les méthodes de relevé, mais que l'hyperstabilité et la concurrence entre espèces peuvent compliquer leur utilisation et l'interprétation des résultats qui en découlent. [Traduit par la Rédaction]

Scoping the Line Up: A Comparison of Biomonitoring Methodologies for Surf Zone Fish Communities

“…However, these capture surveys have known biases that limit their reliability and repeatability. Hook and line fishing surveys are often species-specific due to the choice of tackle and bait, and observer skill affects capture rates [21]. Wave and weather conditions can affect seine surveys by reducing the capture efficiency of nets and creating hazards to researchers in heavy surf (Table 1).…”

Ecological responses to blue water MPAs

“…Truncating the fishing grounds within the treatment zones to retain areas with lower relative abundance of apex predators may have resulted in the remaining fishing grounds in the treatment zone having relatively lower predation pressure and competition for prey and higher local abundance of longnose lancetfish and possibly other lower trophic level species [38]. Displacing fishing effort to grounds with lower relative abundance of top pelagic predators may also have resulted in the remaining fishing grounds in the treatment zone having relatively lower gear saturation and interference competition [49][50], contributing to causing the observed longnose lancetfish standardized catch rate to be higher than the counterfactual prediction.…”

Effect of pelagic longline bait type on species selectivity: a global synthesis of evidence

“…For example, if blue sharks have a higher depredation rate of squid bait relative to forage fish bait, then this would result in overestimating other species' relative risk of capture on fish relative to squid bait due to squiddepredated baitless hooks being counted as available squid-baited hooks. This is similar to how gear saturation can result in underestimates of abundance when interpreting pelagic longline nominal catch rates (Ward 2008;Kuriyama et al 2019). For some pelagic predators, the size of the species used for bait can affect their catch risk.…”